This invention relates to a novel controlled release pharmaceutical preparation and a method for producing the same.
Heretofore, there has been known pharmaceutical preparations in which drug-containing cores are coated with compact films of hydrophobic polymeric substances.
Such preparations have advantages in that they have excellent water resistance, light resistance, humidity resistance, abrasion resistance, storage stability, etc.
However, a preparation having a compact film of a hydrophobic substance has disadvantages in that it has a slow releasing rate of the inner drug and also that the drug cannot be completely released.
In other words, release of a drug is a result of the difference in concentration or osmotic pressure between the inside and outside of the preparation which is created by the dissolution of the drug to a saturated concentration with the digestive fluids having penetrated into the inside through the film. However, since the compact film of a hydrophobic substance scarcely has open space, permeation of the fluid into the film is slow, and even when an osmotic pressure difference enough to release the drug may be created, the dissolution speed is not sufficient because of the small total area of the open space contributing to the release.
As to the method for solving this problem, there has been known a method in which particles of a water-soluble substance are embedded in the film of a hydrophobic polymeric substance so that the film may become porous in the digestive organs by dissolution and elimination of said water-soluble substance.
However, this method is still disadvantageous in that a special contrivance is required for embedding a water-soluble substance in the film, and that it is necessary to use various additives such as dispersing agents, plasticizers, anti-aggregating agents, etc. which make the recipe complicated. Moreover, even if the film may become porous in the digestive organs, its porosity will be affected by the particle size of the water-soluble substance or the degree of dispersion of said substance in the film, and therefore the porosity cannot be necessarily controlled accurately.